How does the way a buffer stabilizes ph during addition of acid differ from the way the same buffer stabilizes ph during addition of base?

Buffer solution is made up of weak acid or base with its conjugate salt. It resists the change in pH of the solution. When acid or base is added to the buffer solution, the pH gets stabilized but the direction of reaction is opposite. Thus, the reaction is same but the one moves backward and other moves in forward direction.

A buffer solution can be defined as:

HA + NaA

Here, NaA is in dissociated form as follows:

NaA/rightarrow Na^{+}+A^{-}

when acid is added it reacts with A^{-} to form HA and reaction moves in backward direction. When base is added it reacts with HA to form more A^{-} and reaction moves in forward direction.

If acid is added

Buffer, is defined as a mixture of a conjugate acid-base pair that can resist changes in pH when small volumes of strong acids or bases are added.

For example in a buffer of carboxylic acid (CH₃COOH) and its conjugate base (CH₃COO⁻):

on the addition of strong acid, the acetate ions neutralize the hydronium ions producing acetic acid (which is already a component of the buffer).

And on addition of strong base, acetic acid consumes the hydroxide ions producing acetate ions (which is also already a constituent of the buffer).

So no change in pH will be there.

While in the buffer of weak base (NH₃)) and and its conjugate acid (NH₄⁺).

On addition of strong acid, ammonia neutralizes the hydronium ions producing ammonium ions that is already a component of the buffer.

While, on addition of strong base, ammonium ions consume the hydroxide ions producing ammonia that is already a constituent of the buffer.

So no change in pH will be there.

Thus the way a buffer stabilizes pH during addition of acid differ from the way the same buffer stabilizes pH during addition of base.